Organic luminescent elements have been drawing attention as thin luminescent materials.
Organic luminescent elements containing organic electroluminescent (EL) materials (hereinafter, also referred to as “organic EL elements”) are thin perfect solid-state elements that can radiate light in response to a low voltage of several to several tens of volts and have many advantages such as high luminance, high luminescent efficiency, small thickness, and small weight. Such organic EL elements have drawn attention as backlights in various displays, display boards of notices and emergency lights, and surface-emitting luminescent bodies of light sources for lighting.
Such an organic EL element includes two electrodes and an organic functional layer that includes at least a light emitting layer and is disposed between the electrodes. The light generated at the light emitting layer passes through one of the electrodes and radiates to the exterior. Accordingly, at least one of the electrodes may be a transparent electrode that transmits light. Organic EL elements generally achieve high luminance from low electric power and have the advantages of superior visibility, a high response rate, a long lifetime, and low power consumption.
A proposed method of forming an emission pattern in such an organic EL element involves irradiating predetermined regions in an organic functional layer with adjusted doses of light so as to modify the functions of the predetermined regions in the organic functional layer, and forming an emission pattern having a gradation of emission luminance levels corresponding to the modified level of the function of the organic functional layer (for example, refer to PTL 1). In such a method, ultraviolet rays are radiated on the presumption that an increase in the cumulative dose, which is the product of ultraviolet intensity and exposure time, causes an increase in the modified level of the function of the organic functional layer.
The inventors discovered that, in formation of an emission pattern in an organic EL element through light irradiation, different relationships between light intensity [W/cm2] and exposure time [s] achieve different modified levels of the function of the organic functional layer, even if the organic EL element is irradiated with a constant cumulative dose [W·s/cm2] of the light.
Thus, irradiation of the organic EL element with focus on only cumulative dose may not yield an emission pattern having a predetermined gradation of emission luminance levels, depending on the relationship between light intensity and exposure time.